This invention relates to a micro relay for switching an electric current on and off.
Conventional relays, for example electromagnetic contactors, are electromagnetically operated switches having a moving contact piece, which is operated by the interaction of an electromagnet with a moving part of its core. Instead of providing a detailed description of this prior art, reference is made, by way of example, to xe2x80x9cNew Electromagnetic Contactor with Wide Control Voltage Rangexe2x80x9d by P. Stephansson, H. Vefling, G. Johansson, Cl. Henrion in ABB Review 1/1997, pages 29 et seq.
As an alternative to such conventional relays, what are referred to as micro relays have been developed and investigated recently. The prior art relating to these is contained, for example, in H. F. Schlaak, F. Arndt, J. Schimkat, M. Hanke, Procedure. Micro System Technology 96, 1996, pages 463-468. Reference is also made to: R. Allen: xe2x80x9cSimplified Process is Used to Make Micromachined FET-like Four-Terminal Microswitches and Microrelaysxe2x80x9d in Electronic Design, Jul. 8, 1996, page 31.
In general, micro relays are mounted on a substrate and have a movable contact piece on the substrate with the contact piece being suspended elastically, and with the drive for the contact piece being operable electrically. The drive, which may, for example, operate electrostatically, electromagnetically or piezo-electrically, is used to move the movable contact piece from an open position to a closed position, or vice versa, with the elastic suspension providing a resetting force. In this case, the individual parts may also be combined, for example with the contact piece having elastic characteristics or being part of the drive.
Micro relays are produced using the known processes from semiconductor technology or comparable micro-engineering processes and, to this extent, are particularly suitable for integration with other semiconductor devices, in particular integrated circuits or transistors.
In addition, particularly in comparison to conventional electromagnetic relays, micro relays have extraordinarily fast response times, owing to the small moving masses. At the same time, the switching power levels required are very low, so that considerable power savings can be achieved, particularly when using a number of them in a relatively large circuit.
Furthermore, in many applications, it is of considerable interest that, since they are physically small, modern micro relays not only occupy small physical volumes but also have correspondingly low weights. Finally, when suitably encapsulated, they are extraordinarily insensitive both to mechanical loads and to thermal loads, once again owing to their small physical size and the small moving masses. Technicians therefore have very much more flexibility when using micro relays than with conventional electromagnetic relays.
The invention is based on the technical problem of finding a micro relay which is better than the prior art.
The invention solves this problem by means of a micro relay having a substrate, a movable contact piece on the substrate, an elastic suspension of the movable contact piece and an electrically operable drive for the movable contact piece, characterized in that the movable contact piece can be moved essentially parallel to the substrate, in the suspension, by the drive, and by a process for producing a micro relay of the type mentioned above, in which the movable contact piece with at least one major part of its functional structure in the form of a two-dimensional structure in a plane parallel to the substrate.
Particular refinements of the invention are the subject matter of the dependent claims.
The micro relay according to the invention is thus distinguished by the fact that the movable contact piece has a movement direction parallel to the substrate. The movable contact piece thus, to a certain extent, moves in a planar fashion and not, as in the prior art, more or less at right angles to the plane of the substrate. This results in various options for technical improvements. Firstly, the entire micro relay can be designed to be essentially two-dimensional, which considerably simplifies the use of typical microtechnological processes, in particular with regard to the necessary lithography, etching and coating steps. Secondly, this makes it possible to avoid parts of the micro relay projecting to a relatively major extent from the micro relay in the direction at right angles to the plane of the substrate, thus impeding subsequent lithography steps, for example in conjunction with adjacent microelectronic circuits. Finally, a flat structure can also simplify the possibilities for subsequent encapsulation or protection by a cover or the like.
In particular, it is preferable to design the structure of the micro relay to be two-dimensional, either as far as possible in its entirety or else partially, that is to say the structure of the movable contact piece, of the drive or of the elastic suspension. This means that, when designing the geometry, those structural elements which govern the function are chosen to be two-dimensional in the substrate plane and, accordingly, can be produced easily and in a standard manner using lithography and structuring.
It is thus advantageous to work with buried layers under the layer which forms the parts that are constructed two-dimensionally to this extent, in which case the buried layers can be removed at suitable points, in order to detach specific parts from the substrate and hence, for example, to design them such that they are elastic or movable.
With regard to the parallelity of the technology with microelectronic processes, silicon may be used as the structure material, not least because, with appropriate doping and depending on the requirement, it can also be designed to be virtually insulating or else electrically conductive. This can also be done in a manner matched to the micro relay structure, by means of appropriate implantation or diffusion steps.
Buried layers may be composed, for example, of silicon dioxide, to be precise likewise to maximize the points of contact with the established semiconductor processes.
When using silicon on silicon dioxide or some other insulator, SOI (silicon on insulator) structures which have been introduced can be made use of in this case, in particular when monocrystalline silicon is preferred as the basic material, on an SIMOX wafer.
The advantageous structuring processes for two-dimensional structuring of the micro relay are generally ion etching processes and, in particular, RIE processes. Assuming the process is controlled appropriately, ion etching processes allow virtually vertical flanks to be produced in various materials, with depths which are completely sufficient for this application. These processes are furthermore uniform, even when the surfaces to be processed are relatively large, and are highly suitable for automated mass production. In addition to other established ion etching processes, the RIE process is distinguished by a large choice of known processes for widely differing materials, while the hardware complexity is at the same time acceptable, and the etching rates are relatively high.
For a technological example relating to this, reference shall be made to xe2x80x9cVertical Mirrors Fabricated by Deep Reactive Ion Etching for Fiber-Optic Switching Applicationsxe2x80x9d by C. Marxer et al., Journal of Microelectromechanical Systems, Volume 6, No. 3, September 1997, pages 277-285. This document describes microoptical switches for fiber-optic applications, which have been structured by means of an RIE process in silicon on buried silicon dioxide layers with 75 xcexcm-high vertical walls. The disclosure in this document is included here by way of reference.
A contact surface of a contact piece can be connected to the drive by means of a rod which is arranged parallel to the substrate and preferably has a lattice structure, in order to achieve good robustness with low weight. This allows structures to be produced which are insensitive to vibration and shock, respond quickly and have high resonant frequencies. With respect to the two-dimensional structure which is preferred for this invention, this lattice structure can be produced in an advantageous manner by two-dimensional structuring of the micro relay.
Furthermore, the movable contact piece may have an oblique contact surface, to be precise a surface which runs obliquely with respect to the movement direction while at the same time runs essentially at right angles to the plane of the substrate. The oblique arrangement of the contact surface can result in a relatively large contact area when in contact with a corresponding, complementary contact surface of a stationary contact piece, without the movable contact piece needing to have an excessively large physical extent. At the same time, the oblique angle enclosed between the movement direction and the contact surface can also result in the power of the drive being stepped up, especially if there is a corresponding second contact surface, or some other contact point, on the side of the movable contact piece opposite the contact surface.
If the movable contact piece or a stationary contact piece is designed such that it results in a detectable transverse component between respective contact surfaces, that is to say a movement component in the surface direction, during the closing movement, for example by one contact piece bending, this allows the contact quality to be improved.
An electrostatic configuration is preferable for the drive, since, in comparison to electromagnetic or piezoelectric drives, it has the advantage of both low supply powers and low supply voltages. In order to compensate for the fundamental disadvantage of electrostatic drives, namely the relatively low drive forces, a finger structure is preferred, which is arranged in a toothed manner, and can actually be produced in a worthwhile manner during the two-dimensional structuring discussed according to the invention.
The elastic suspension is preferably provided by at least one meandering web. The details of these geometric shapes will be explained in more detail in the description of the exemplary embodiment.
Finally, the invention also provides the possibility of incorporating an arcing chamber structure, which is known from conventional circuit breakers, as is described in more detail in the third exemplary embodiment.
As stated, the invention relates both to a novel micro relay structure and to a two-dimensional structuring process designed for this purpose. Accordingly, the above statements relating to the various individual aspects of the invention should be understood as relating both to the disclosure of appropriate apparatus features and to process features.